Relaxation oscillation generator



Aug. 26, 1941. c. l.. FAUDELL RELAXATION OSCILLATION GENERATOR FiledNOV. 1, 1958 M94 l "Jr l N D l f5 'IZ-CT/A( INVETOR CHARLES ESL/5FAL/DELL :E'' BvY ATTORNEY' Patented Aug. 26, 1941 UNITED STAT ES PATENTFICE f A i 2,254,031 `l Y j i v Rx'iLAXAT16NV ko`so1LLA'rIo1\i 'G'EERATRj Charles Leslie Fanden, stokertgesmngiand, as; signor to ElectrietMusicallndustries Limited,A .A i Y Hayes, Middlesex, England, a

Britain Apiiieat'ioii November 1, 15138, sniair'N'o.1,238,181 i I InGreat Britain November 3;-19312 I solaims.. (Crest-feel This inventionrelates to relaxation oscillation generators for "generatin5g`substantially Saw tooth oscillations. Thesegeer'ator's may comprise acondenser which is charged froin a current souroe and discharged bymeans of a thermionic valve; the relatively slovf' charge forming thelong ank of the saw tooth 'and lthe relatively quick dischargefoimiiigithe short flankof the' saw tooth.

Alternatively', the generators 'may comprise a condenser Whieh isdischarged slowly to lform the long' flank of the saw tooth 'aridcharged quickly through a tnenfiioie vai've to: form the shortV flank ofthersavv tooth. In soi'rie casesfin order to provide fa' push-pulloutput the'generator may comprise two eo'ridnsei-s, onev oiwhichischarged slowly a'nd diseh'arg'ed quickly and the other Which isdisehage'd slowly and charged Quickly. The v'oltae set ii'p'cros's theordenrse'r is amplied by a further valvefnd the frequency of theoscillations is controlled by means of con` trolling pulses.

Oscillation generators of this kind can be em= ployed for a variety ofpurposes, butth'ey are Ye'specially 'applielbl'e for'v use in televisinsystems', the 'controlling' pulses being" theV synchronising pulsesnr'xiially used in television' systems. Iii 'some cases it may be foun'dthat the con trolling purses which is appued to the 'valve is ofYS11-oli a Sinall amplitude that it' fails to 'control the oscillationgenerator.

It is the chief object' `of the present invention to provide animp-roved's'cillatiii generator of the above kind in lWhich thegenerator is cori trolled despite the controlling impulses being ofrelatively sm'all amplitude.

A'ccordi'ig' to the present invention, there i's provided an impedancedevic'e ass'oeiated With a sduroe of charging current and with athermionic valve whioh is arranged so that Wheriv controlling pulses areapplied to said valve substantially saw tooth Waves are set upY by saidimpedance device and wherein an amplifying :circuit is provided in'cluding afu'rther' thermioniovalve for amplifying the saw tooth Waves,the arrangement being 'suoh that said rst r'nentioned valve,y orsubstantially simultaneously with the application. of said pulses to therst' valve, are applied to said further valve so as to be' amplifiedthereby and then applied to said rst valve so that the generator can becontrolled by .pulses of relatively small amplitude.

The invention is particularly applicable for use With the kind ofcircuit disclosed in my c'o-pen'd'- ing United States application SerialNo. 185,493, filed January 18, 1938,v patented on August 27,

1946 asqPatent'No.. 212,933; Where' the -sxnoh'roe nisingpulsesderived-from, the 'separating 'circuit dsclosedririfthis'fspeicationinaybe of relatively sriial'l amplitude; "otx the Jorder ofi. 'about 'oneEVolt;

nIn one forni'of1 the-invention thev controlling pulses'l'nay beappliedaeross'a'resistance disposed between theeathod'e ofthe'rst valvevand earth, thescondenserlwhich'is chargei, asv above stated; beingeonneetedbetw'een the cathode andof Asaid resistance vandtheanod'e'offthe valve.V In vanother form ofi the. invention kthe'controlling pulses may be applied across ajresistanee connected betweenthe anode oftherstgvalvejzandearth and ar 'ranged in series withthesaidcondenser.-

In order that-the invention vmay be clearly understood and I readilycarried into. effect, it will now be rnore fully described with.reference Yto the aooornpanyig ,drawin, in'. which:

,o Figrel llustrat' ',anvosoillator constructed in y Figure 2 illustraea part, di` .the ciicmt 'shown yin Figure 1 enitouy'iga modiiieation, iy

y tratesa rhodifiedforin of oscillator fcllit emply ,gia gasjd tes tn`application of the in- .iti 'tnefeitwina the n vicates vhe iirstvalv'ethe netted through aiesistanee Si the; rsiiii ,o maar@ Surtof anode Tjot ist the lQatar-trieofthe valveis' eo ed thro ghar'sistano'e J tothenegative terminalforf Ythe, anode current source' whieiiiiaijtiiidl. 1 At t B'tri'the'eath enti' of the 'resistance l andthe ai n waive( S' is acondenser ya 'whi is periodically reed from they anode current soireeandV discharged when the valve 5k s-rideied", tiiig-4 as'herenafterreferred v node f the valve ,Bij is Ycoin'eotevd 'ser er lvalve I6, leakresistance asshotvnf, The cathode of nf tt. .theseaiimiigfceiieliiiaicated at It. A tare t6 the eontroigrie 'of thentedit'ifroug'ii a variable rea ping on the choke coil I3 is connectedto the grid of the valve 5 through a blocking condenser I6 which isassociated with a leakage path comprising a variable resistance I 1.Controlling or synchronising pulses are applied 'across the resistance 1from terminals I8. In operation of the circuit the valve 5 is normallynon-conducting and during this period the condenser 8 charges throughthe resistance 6 positively, the positive potential across the condenser8 being applied to the Valve I and amplified, the amplied saw-toothcurrent being fed through the scanning coils I5. On receipt of acontrolling pulse the valve is caused to conduct to discharge condenser8, conduction of the valve 5 occurring until the condenser I6 assumessuch a charge due to the interaction of vthe valves 5 and I0 that anodecurrent ceases to flow` through the valve 5. The charge across condenserI6 leaks away through the resistance I1. Since the controlling pulsesare applied: across the resistance 1, the upper end of which isconnected to the condenser 8, the controlling pulses are appliedsimultaneously to the valve 5 and to the valve I0, the latter valveamplifying the controlling pulses which are applied from the coil I3 tothe grid of the Valve 5. In this manner, despite the fact that thecontrolling pulses may be of relatively small amplitude, the valve 5rapidly reaches the condition in which it is rendered conducting todischarge the condenser 8 due to the amplication of the controllingpulse by the valve III. Charging of the condenser 8 generates the longflank of the saw-tooth voltage Y wave whilst discharge of th-e condensergenerates the short flank. The circuit shown in Figure 1 isself-oscillatory in the absence of controlling pulses, the latter beingemployed for synchronising purposes to initiate the discharge. Theeffect of a small amplitude controlling pulse if it were not for thelamplification of the pulse which occurs according to the invention.would be to make the freonency adiustment (resistance I1) very criticaland moreover, there would be no margin to allow for natural frequencydrift.

Figure 2 of the drawing illustrates a modification of the circuit shownin Figure 1. in which instead of the resistance 1.bein er connectedbetween cathode and earth and the condenser 8 connected to the cathodeof the valve 5 las shown in Figure 1, a resistance 21 and condenser 28are arranged in series between the anode and cathode of the valve 5. Theother components of the circuit which are not shown will be arranged asin Figure 1. In this case therefore the controlling pulses are appliedrst to the valve I 0 which is not shown in Figure 2. 'Ihe `arrangementshown in Figure 1 is, however, advantageous compared with that shown inFigure 2, since the potential drop across the resistance 1 duringconduction of the valve 5 is partially neutralised by the potential riseduring conduction thus avoiding a disturbing feedback into the sourcefrom which the controllingpulses are obtained. I

It is assumed in Figures 1 and 2 that lthe controlling pulses areapplied to the terminals I8 in the negative sense, but ln the case wherethe output from the valve I 0 is applied through a transformer to thescanning coils as shown in Figure 3 hereinafter referred to, thecontrolling pulses may be applied either in a positive or a negativesense according to the point at which the condenser I6 is connected tothe Secondary 75 of the transformer for the feed-black of the amplifiedcontrolling pulses.

Figure 3 of the vdrawing illustrates the invention as applied to acircuit in which the rst valve is a gas-discharge valve, such as a valveof the kind known by the registered trade-mark Thyratron 'In this figurethe elements which are equivalent to corresponding elements in Figures 1and 2 have been given the same reference numerals. In this case the rstvalve, which as stated above, is a gas-discharge valve, is indicated 'atI9 and a variable self-biasing resistance v31 is Vconnected betweencathode and earth and vshunted by a decoupling condenser 2D in serieswith a biasing resistance 2|. Controlling pulses are applied toterminals I8 across a resistance 31 which is in series with a condenser38 connected between the anode of the valve I9 and earth. The outputfrom Ithe valve I6 is applied to the scanning coils I5 through atransformer 22 the secondary of the transformer being connected to earththrough a condenser 36 and resistance 23 whilst the grid of valve I9 isconnected to the junction between condenser 36 |and the resistance 23 sothat the controlling pulses applied to the valve I6 are fed back afteramplification to the grid of valve I9. The applied controlling pulsesmay be either in the positive ornegative sense according to theconnection of the condenser 36 to either the positive or negative end ofthe transformer secondary winding. Discharge of the valve I 8 occurswhen the anode potential (i. e. the charge across condenser 38) reachesa critical value in relation to the fixed bias imposed by resistance 21.For synchronising purposes the value of the resistance 21 is adjusted sothat the controlling pulse is applied justfprior to the instant when thevalve I 9 would conduct in the absence of the controlling pulse.

Figure 4 of the drawing illustrates the invention as applied to ablocking oscillator and the parts which are equivalent to thecorresponding parts of Figures l, 2 and 3 have been given the samereference numerals. In this example, the first valve 24 is of the screengrid type and the screening grid and the control grid are coupledtogether through a transformer 25 so that when the valve 24 is caused toconduct on application of an amplified controlling pulse from the valveI0 oscillation of the valve 24 is initiated and continues until theblocking condenser 46 assuines such a potential that the valve 24 isbiased to cut-off. In Figure 4 the output from the valve I0 is appliedto thescanning coils I5 from a transformer 22 and the secondary windingof the transformer 22 in this case is connected through the condenser 46to the screening grid of the valve 24. In this example also a resistance41 and condenser 48 are arranged as shown in Figures 2 and 3. Positiveor negative controlling pulses may be applied according to theconnection of the condenser 46 tothe secondary winding of thetransformer 22. The value of the condensers 36 in Figure 3 or ofcondenser 46 in Figure 4 may be quite small since it is only normallynecessary to apply the higher frequency of the leading edge of thecontrolling pulse to the circuit in order to intiate the dischargeperiod of the valves I9 and 24.

The condenser 46 provides a positive feed back as in thecase ofFigure 1. This is liable to modify the frequency of the blockingoscillator, especially with changes of amplitude. It is therefore anadvantage to take the amplified pulse from the secondary winding inopposite phase and connect the condenser I6 to the screen of the valve24.

The invention in the above embodiments has been described with referenceto the generation of saw-tooth currents for the scanning coils l5,although it will be appreciated that the invention will also be appliedfor the generation `of substantially saw tooth potential waves for, forexample, electrostatic deflection of a cathode ray beam.

Although in the above embodiments the condenser is charged slowly toprovide the long flank of the saw tooth and discharged quickly through athermionic valve to provide the short flank, it is obvious that thisinvention may be applied to relaxation oscillation generators of thetype in which a condenser is charged quickly through a thermionic valveto produce the short flank of the saw tooth and discharged slowlythrough a resistance shunting the condenser, to provide the long ank. Anexample of this type of generator is shown in Figure 1 of thespeciiication of British Patent No. 471,737. In accordance with thisinvention, the saw tooth Voltage set up across condenser I5 of thisfigure would be amplied by a further valve and controlling pulsesapplied in such a manner that they would be amplied by said furthervalve and then applied to the grid of Valve lli.

In Figure 5 of the specification of British Patent No. 471,737 there isshown a relaxation oscillation generator from which a push-pull outputis obtained. The condenser i3 is charged slowly and discharged quickly,whereas condenser 38 is charged quickly and discharged slowly. Inaccordance with this invention the voltages across condensers 38 and d3would be amplified by means of a suitable push pull amplifier and thecontrolling pulses applied to the arnplier in suchk a manner that theywould be ampliiied and fed back to the grid of valve 35. The controllingpulses may be for example fed to the push-pull amplifier by means of atransformer and amplified pulses fed back through a transformer or fromacross the load of one oi the valves of the push-pull amplier.

I claim:

1. A sawtooth wave generator comprising a condenser, a iirst thermionicvacuum tube having anode, cathode and at least one control electrode,said condenser being shunted across the anode and cathode of saidthermionic tube, a resistance connected serially between said cathodeand a point of fixed reference potential, said condenser beingelectrically connected to said point of fixed reference potential, meansjoining the control .electrode of said thermionic vacuum tube to thepoint of xed reference potential, a second thermionic vacuum tube havinganode, cathode and at least one control electrode, means for couplingthe storage condenser and resistance to the control electrode of saidsecond thermionic vacuum tube, an inductive member connected in theanode-cathode circuit of said second thermionic vacuum tube, and meanscoupling said inductive member to the control electrode of said rstthermionic vacuum tube.

2. Apparatus in accordance with claim 1 wherein there is provided inaddition means for impressing signals from an external source onto theresistance lmember connected serially between the cathode and the pointofV xed reference potential in said first thermionic vacuum tube.

3. A sawtooth Wave generator comprising a condenser, a rst thermionicvacuum tube having anode, cathode and at least one control electrode,said condenser being shunted across the anode-cathode space dischargepath thereof, a point of xed referencev potential, an impedance memberconnected between said cathode and said point of fixed referencepotential, a second thermionic tube having anode-cathode and at leastone control electrode,`means for applying the voltage across saidcondenser and impedance to the control electrode-cathode circuit ofsecond thermionic tube, whereby variations in potential of saidcondenser` are impressed on to the control electrode-cathode circuit ofsecond thermionic tube, and means for feeding back a portion of theenergy developed in the output circuit of said second thermionic tube tothe control electrode'of said first thermionic tube.

vCI-IPJtLES LESLIE' FAUDELL.

